Optical layers, films and systems

Abstract

An optical system includes an extended illumination source configured to emit light from an extended emission surface thereof and a light redirecting layer disposed on the extended emission surface. The light redirecting layer has a structured major surface that includes a regular array of light redirecting structures, each light redirecting structure including a plurality of facets; and a plurality of discrete spaced apart window segments. The optical system includes a plurality of reflective segments where each reflective segment is disposed on a corresponding window segment. For substantially normally incident light, each reflective segment has a total: average optical reflectance of at least 30% in a visible wavelength range extending from about 420 nm to about 650 nm; and optical transmittance of at least 10% for at least one infrared wavelength in an infrared wavelength range extending from about 800 nm to about 1200 nm.

What is claimed is: 
     
       1. An optical system, comprising:
 an extended illumination source configured to emit light from an extended emission surface thereof, and comprising:
 at least one light source; and 
 a reflecting layer spaced apart from, and substantially co-extensive with, the extended emission surface, the reflecting layer configured to reflect incident light that is emitted from the at least one light source toward the extended emission surface; 
 a first light redirecting layer defining a plane of the first light redirecting layer and disposed on the extended emission surface and comprising a first structured major surface opposite a second major surface, the first structured major surface comprising: 
 a regular array of first light redirecting structures, each first light redirecting structure comprising a plurality of first facets making oblique angles with the plane of the first light redirecting layer; and 
 a plurality of discrete spaced apart first window segments substantially parallel to the plane of the first light redirecting layer; and 
 a plurality of first reflective segments, each first reflective segment disposed on, and substantially co-extensive with, a corresponding first window segment, such that for substantially normally incident light, each first reflective segment has a total: 
 average optical reflectance of at least 30% in a visible wavelength range extending from about 420 nm to about 650 nm; and 
 optical transmittance of at least 10% for at least one infrared wavelength in an infrared wavelength range extending from about 800 nm to about 1200 nm. 
 
 
     
     
       2. The optical system of  claim 1 , wherein the extended illumination source comprises:
 a lightguide for propagating light therein along a length and width of the lightguide, the lightguide disposed between the reflecting layer and the first light redirecting layer and comprising the extended emission surface; and 
 the at least one light source disposed proximate an edge surface of the lightguide, the reflecting layer configured to reflect light that exits the lightguide toward the reflecting layer, the reflected light propagating toward the first light redirecting layer. 
 
     
     
       3. The optical system of  claim 1 , wherein the extended illumination source comprises:
 a first optically diffusive layer for scattering light and comprising the extended emission surface, the first optically diffusive layer and the reflecting layer substantially coextensive with each other and defining an optical cavity therebetween; and 
 the at least one light source disposed in the optical cavity. 
 
     
     
       4. The optical system of  claim 1 , wherein for each first reflective segment and for substantially normally incident light, at least 70% of:
 the total average optical reflectance of the first reflective segment in the visible wavelength range is specular optical reflectance; and 
 the total optical transmittance of the first reflective segment for the at least one infrared wavelength in the infrared wavelength range is specular optical transmittance. 
 
     
     
       5. The optical system of  claim 1 , wherein each first light redirecting structure in the regular array of light redirecting structures is a linear structure, wherein the first facets of the first light redirecting structure extend along a length direction of the first light redirecting structure, the first light redirecting structure having a length L and a width W, L/W>10. 
     
     
       6. The optical system of  claim 1 , wherein at least one first window segment in the plurality of first window segments is a land segment between two adjacent first light redirecting structures in the regular array of first light redirecting structures. 
     
     
       7. The optical system of  claim 1 , wherein at least one first window segment in the plurality of first window segments is a top segment of a truncated first light redirecting structure in the regular array of first light redirecting structures, the at least one first widow segment connecting the plurality of first facets of the truncated first light redirecting structure to each other. 
     
     
       8. The optical system of  claim 1 , wherein each first reflective segment comprises a metal. 
     
     
       9. The optical system of  claim 1 , wherein each first reflective segment comprises a plurality of stacked layers, each layer having an average thickness of less than about 500 nm. 
     
     
       10. The optical system of  claim 1  further comprising:
 a second light redirecting layer defining a plane of the second light redirecting layer and disposed on the first light redirecting layer and comprising a third structured major surface opposite a fourth major surface, the third structured surface comprising:
 a regular array of second light redirecting structures, each second light redirecting structure comprising a plurality of second facets making oblique angles with the plane of the second light redirecting layer; and 
 a plurality of discrete spaced apart first second window segments substantially parallel to the plane of the second light redirecting layer; and 
 
 a plurality of second reflective segments, each second reflective segment disposed on, and substantially co-extensive with, a corresponding second window segment, such that for substantially normally incident light, each second reflective segment has a total:
 average optical reflectance of at least 30% in the visible wavelength range; and 
 optical transmittance of at least 10% for the at least one infrared wavelength in the infrared wavelength range. 
 
 
     
     
       11. The optical system of  claim 1 , wherein for substantially normally incident light and for each of mutually orthogonal first and second polarization states, the reflecting layer has a total:
 average optical reflectance of at least 80% in the visible wavelength range; and 
 optical transmittance of at least 20% for the at least one infrared wavelength in the infrared wavelength range. 
 
     
     
       12. A structured optical layer defining a plane of the structured optical layer and comprising:
 a structured surface comprising a regular array of first segments, each first segment making an angle from about 30 degrees to about 60 degrees with the plane of the structured optical layer, and a plurality of second segments, each second segment making an angle of less than about 10 degrees with the plane of the structured optical layer; and 
 a multilayer film disposed on each of at least a majority of the second segments, each layer in the multilayer film having a thickness less than about 500 nm, such that for substantially normally incident light, the multilayer film has a total: 
 average optical reflectance of at least 50% in a visible wavelength range extending from about 420 nm to about 650 nm; and 
 optical transmittance of at least 30% for at least one infrared wavelength in an infrared wavelength range extending from about 800 nm to about 1200 nm. 
 
     
     
       13. An optical system, comprising:
 an extended illumination source configured to emit visible light in a wavelength range extending from about 420 nm to about 650 nm from an extended emission surface thereof, and comprising: 
 at least one light source configured to emit visible light; and 
 a reflecting layer spaced apart from, and substantially co-extensive with, the extended emission surface; 
 a liquid crystal display panel disposed on, and substantially co-extensive with, the extended emission surface, and configured to form a visible image for viewing by a viewer; 
 a reflective polarizer disposed between the extended illumination source and the liquid crystal display panel; and 
 at least one light redirecting layer disposed between the reflective polarizer and the extended illumination source, and comprising a regular array of linear prismatic structures extending along a first direction and arranged along an orthogonal second direction, the at least one light redirecting layer increasing a brightness of light exiting the optical system along a normal direction substantially perpendicular to the optical system by recycling a portion of light emitted by the extended emission surface, such that when an infrared image having an infrared wavelength in a range from about 800 nm to about 1200 nm is incident on the optical system along the normal direction, the optical system transmits at least a portion of the incident infrared image therethrough along the normal direction, such that when the infrared image has a first spatial frequency of at least about 8 line pairs per mm, the transmitted infrared image has a modulation transfer function (MTF) of greater than about 0.5 at the first spatial frequency. 
 
     
     
       14. A light redirecting film comprising:
 a light redirecting layer comprising a first structured major surface opposite a second major surface, the first structured major surface comprising a plurality of substantially parallel linear truncated prismatic structures extending along a first direction and arranged along an orthogonal second direction, each truncated prismatic structure comprising opposing side facets making an angle in a range from about 60 degrees to about 120 degrees with each other, and a top facet substantially parallel to the second major surface and connecting the opposing side facets; and 
 a plurality of multilayer segments, each multilayer segment disposed on, and substantially co-extensive with, the top facet of a corresponding truncated prismatic structure, each multilayer segment comprising a plurality of stacked layers, each layer having a thickness less than about 500 nm, such that for substantially normally incident light, the multilayer segment has a total average optical reflectance of at least 50% in a visible wavelength range extending from about 420 nm to about 650 nm, and a total optical transmittance of at least 30% for at least one infrared wavelength in an infrared wavelength range extending from about 800 nm to about 1200 nm, such that when the light redirecting film is disposed on a Lambertian light source that emits visible light in the visible wavelength range, and has a total average optical reflectance of at least 85% in the visible wavelength range and a first luminance along a direction normal to the Lambertian light source, light transmitted by the light redirecting film has a second luminance along the normal direction, a ratio of the second luminance to the first luminance greater than about 1. 
 
     
     
       15. The light redirecting film of  claim 14 , wherein the ratio of the second luminance to the first luminance is greater than about 1.6.